1. Field of the Invention
The present invention relates to an integrated optical circuit for measuring current based on the Faraday effect, a sensor module comprising such an integrated optical circuit and a measuring device. It further relates to a method for measuring current by an integrated optical circuit.
2. Description of the Prior Art
Fiber-optical current sensors (FOCS) detect the current through a conductor by means of an optical fiber wound around the conductor. The magnetic field surrounding the conductor rotates the oscillation plane of linearly polarized light or causes a phase shift between circular polarization modes, orthogonal to one another, of a light beam, guided through the optical fiber. The amount of the phase shift between the polarization modes caused by the electric current is a measure of the intensity of current in the conductor.
In a fiber-optical current sensor, a light beam generated by a light source is guided to a polarizer via a directional coupler and linearly polarized by the polarizer. The polarized light is coupled at 45 degrees with respect to the polarization axes of a polarization maintaining fiber by a fiber splice so that two different polarization modes comprising approximately the same amplitude are guided in parallel in the same fiber. The two polarization modes are “partial light beams” of a primary light beam. They are guided in parallel, comprising a defined polarization and in each case use another optical light path in the polarization maintaining fiber. The two polarization modes pass through a twin refraction phase modulator, which adjusts a non-reciprocal phase shift between the two polarization modes. A λ/4 phase shifter converts the linearly polarized light into circularly polarized light, to enhance the Faraday effect. The light then passes through a fiber coil, which winds around the conductor carrying the current to be measured, and is reflected in a reflector. When a current flows in the conductor, the Faraday effect between the two circularly polarized polarization modes causes a phase shift whose value is proportional to the current in the conductor. The returning polarization modes are brought together at the fiber splice and guided via the polarizer and the directional coupler to a detector, on which the two polarization modes interfere. The phase shift is reflected in a shift of the interference pattern, which is evaluated.